[platform][zynq] if not initializing sdram and sdram_size == 0, power off the ddr pll
[platform][zynq] if not initializing sdram and sdram_size == 0, power off the ddr pll

also consolidate some debug commands

Change-Id: Ibd10f77f1e536884f7da249d75711099f6d7944b

travisg/lk,sndnvaps/lk,grub4android/lk,minglun-tsai/lk,GCrean/lk,ErikCorryGoogle/lk,littlekernel/lk,sndnvaps/lk,grub4android/lk,skabet/lk,minglun-tsai/lk,sndnvaps/lk,GCrean/lk,srodrig1/lk,littlekernel/lk,littlekernel/lk,hollanderic/lkstuff,skabet/lk,GCrean/lk,ErikCorryGoogle/lk,hollanderic/lkstuff,travisg/lk,nvll/lk,travisg/lk,grub4android/lk,skabet/lk,grub4android/lk,littlekernel/lk,nvll/lk,minglun-tsai/lk,srodrig1/lk,GCrean/lk,skabet/lk,grub4android/lk,nvll/lk,sndnvaps/lk,nvll/lk,travisg/lk,srodrig1/lk,skabet/lk,hollanderic/lkstuff,ErikCorryGoogle/lk,hollanderic/lkstuff,sndnvaps/lk,minglun-tsai/lk,srodrig1/lk,nvll/lk,srodrig1/lk,GCrean/lk,ErikCorryGoogle/lk